1. Field of the Invention
The present invention relates generally to flexible printed circuits, more specifically, it relates to an impedance controlled flexible printed circuit with differential mode transmission lines for high-speed data transmission.
2. Description of the Prior Art
Flexible printed circuits have been widely used in high price notebook computers for connecting the liquid crystal display (LCD) to the main system. Low Voltage differential signals (LVDS) structure has been implemented for high transmission data rate for reducing the power consumption and noise interference. A serious competition comes from micro coaxial cables because of the short prototype producing time, thus, some models of notebook computers have been implemented with micro coaxial cables instead of flexible printed circuits. The micro coaxial cables are not suitable for a bending mode, so the outfit of the main system for cable to penetrate through has been changed from a flat rectangle to a small round or square hole. This change has modified the bending mode to a torsion mode, and it can improve the suitability of the micro coaxial cables. However, the micro coaxial cables lack mass production ability and have low yielding rate as well as low temperature sustaining ability, so some engineers try to switch back from the micro coaxial cables to the flexible printed circuits. But a small round or square hole is no longer suitable for the flexible printed circuits.
This invention has been aimed to solve the above mentioned problem of fitting a planar flexible printed circuit in a non-flat structure constraint so that its application can be more prevalent. The main object of this invention is to convert a planar flexible printed circuit to a multi-planar flexible printed circuit structure. Accordingly, the multi-planar flexible circuit can be better fit in a non-rectangular structure such as a small round or square hole.
Another object of this invention is to form a multi-planar flexible printed circuit in which the impedance of transmission lines can be better controlled. In the present invention, the flexible printed circuit comprises a multi-planar structure including layers of signal conducting elements for differential mode, common mode, power, and/or ground. Transmission lines are organized as groups based on their characteristics. An area containing a pair of signal conducting elements is cut together to form a group in a same layer. Therefore, the impedance of the transmission lines can be controlled.
Other features and advantages of the present invention will become apparent from the following description which refers to the accompanying drawings.